FIG. 1 shows the block diagram illustrating the conventional time-division duplex transmit-receive apparatus having the correction means. The conventional transmit-receive apparatus comprises an antenna array constituted by N (N is an integer equal to or larger than two) antenna elements. Each antenna element is accompanied by a set of transmitting unit-receiving unit pair.
It is now assumed that Ti shows amplitude and phase characteristics of the ith transmitting unit (i is an integer of 1≦i≦N) and Ri amplitude and phase characteristics of the ith receiving unit. The amplitude and phase characteristics Ki of the ith set of transmitting unit-receiving unit pair during a transmit-receive operation can be represented by the following formula 1 in the case that transmit-receive patterns are caused to be matched to each other.Ki=Ri/Ti  (Formula 1)
A given set of transmitting unit-receiving unit pair is selected as a reference set, and the amplitude and phase characteristics of each of the other sets of transmitting unit-receiving unit pair during transmit-receive operation are each determined independently to obtain the relative difference of the determined amplitude and phase characteristics with respect to the amplitude-phase characteristics of the reference set, thereby making it possible to correct the amplitude-phase characteristics of respective sets of transmitting unit-receiving unit pair. If the first set of transmitting unit-receiving unit pair (on leftmost side in the figure) is selected as a reference set, for example, then the correction value Hi for the ith set of transmitting unit-receiving unit pair can be obtained by the following formula 2.Hi=/Ki=/Ti)/(R1/T1)=T1/TiR1  (Formula 2)
That is, if the product of the amplitude-phase characteristic of the transmitting unit in the first set as a reference one and the amplitude-phase characteristic of the receiving unit in the ith set, and the product of the amplitude-phase characteristic of the transmitting unit in the ith set and the amplitude-phase characteristic of the receiving unit in the first set is known, then the correction value Hi for the ith set of transmitting unit-receiving unit pair can be obtained.
The transmission and reception in the conventional transmit-receive apparatus shown in FIG. 1 are carried out alternately in a time-division manner for time sequence as illustrated in a time sequence (a) of FIG. 2. It is also illustrated in a time sequence (b) of FIG. 2 that respective amplitude and phase characteristics of sets of transmitting unit-receiving unit pair are corrected in turn at the time of transmission.
In the conventional transmit-receive apparatus, the terminal A of the first switch SW1-i (1≦i≦N) of the ith set is connected with the terminal T at the time of transmission to radiate transmission power from the transmitting unit T-i through the branching circuit D-i to space by the antenna element AN-i. 
The terminal R of the first switch SW1-i is connected with the terminal S of the forth switch SW4-i, and the terminal R of the forth switch SW4-i is connected with the receiving unit R-i. In the forth switch SW4-i, the terminal R is connected with the terminal A at the time of transmission.
On the other hand, from the branching circuitD-1 of the first set as a reference one, the transmission power from the transmitting unit T-1 is sent to the terminal P of the second switch SW2. The terminals C2 to CN of the second switch SW2 are connected with the terminals A of the fourth switches SW4-2 to SW4-N, respectively.
The branching circuits D-2 to D-N receive the transmission powers from the transmitting units T-2 to T-N, respectively. The transmission powers are subsequently sent to not only the antenna elements AN-2 to AN-N but also the terminals C2 to CN of the third switch SW3, respectively. The terminal P of the third switch SW3 is connected with the terminal A of the fourth switch SW4-1 of the first set.
The switches SW2 and SW3 are operated in an interlocking manner. That is, the switches SW2 and SW3 are respectively switched toward the terminals C2 at the time of first transmission, toward the terminal C3 at the time of second transmission, toward the terminal C3 at the time of third transmission, . . . , toward the terminal CN at the time of (N−1)th transmission.
According to the connection structures of the switches and the switching operations thereof described above, it is understood that at the time of first transmission, a part of the transmission power from the transmitting unit T-1 of the first set is applied to the receiving unit R-2 of the second set through the branching circuit D-1, the terminals P-C2 of the second switch SW2, and the terminals A-R of the fourth switch SW4-2 of the second set, while a part of the transmission power from the transmitting unit T-2 of the second set is applied to the receiving unit R-1 of the first set through the branching circuit D-2, the terminals C2-P of the third switch SW3, and the terminals A-R of the fourth switch SW4-1 of the first set.
At the time of second transmission, a part of the transmission power from the transmitting unit T-1 of the first set is applied to the receiving unit R-3 of the third set through the branching circuit D-1, the terminals P-C3 of the second switch SW2, and the terminals A-R of the fourth switch SW4-3 of the third set, while a part of the transmission power from the transmitting unit T-3 of the third set is applied to the receiving unit R-1 of the first set through the branching circuit D-3, the terminals C3-P of the third switch SW3, and the terminals A-R of the fourth switch SW4-1 of the first set.
In the same way, at the time of (N−1)th transmission, a part of the transmission power from the transmitting unit T-1 of the first set is applied to the receiving unit R-N of the Nth set through the branching circuit D-1, the terminals P-CN of the second switch SW2, and the terminals A-R of the fourth switch SW4-N, while a part of the transmission power from the transmitting unit T-N of the Nth set is applied to the receiving unit R-1 of the first set through the branching circuit D-N, the terminals CN-P of the third switch SW3, and the terminal A-R of the fourth switch SW4-1 of the first set.
In this manner, T1Ri and TiR1 in the formula 2 can be known by determining the output signals of the respective receiving units after applying the transmission power from the transmitting unit of the first set to the receiving unit of the ith set, and applying the transmission power from the transmitting unit of the ith set to the receiving unit of the first set. Therefore, the output signals of respective receiving unit R-i are applied to the arithmetic circuit 30 to calculate the amplitude and phase characteristics correcting values, thereby obtaining the correction value Hi in the formula 2. Using the correction value Hi, the arithmetic circuit 40 calculates weighting factors for correction. The amplitude and phase characteristics of the transmitting unit T-i of the ith set can be corrected by the weighting factors thus obtained, thereby making it possible to eliminate the dispersions of amplitude and phase characteristics between the sets of transmitting unit-receiving unit pair to have respective transmission and reception patterns conformed (see Japanese Patent Publication No. 2000-216618, paragraphs 0031 to 0047, FIGS. 2, 7, 14, for example). In FIG. 1, reference numeral 50 indicates the directionality control and arithmetic circuit.